SC14-15-16 Flashcards
What is the yield?
The amount of product you get from a reaction.
What does percentage yield compare?
Actual and theoretical yield.
What’s the equation for percentage yield?
Actual yield / theoretical yield X 100
What is the theoretical yield?
Its the maximum mass of product that could be made, based on the balanced equation.
Why will the percentage yield never be 100%?
Not everything has reacted.
Leave bits on equipment/loss of product
Unwanted products - side reactions (might react with other chemicals)
What is atom economy?
Shows how much of the reactant mass is converted into useful products.
What’s the equation for atom economy?
Total Mr of desired products / total Mr of all products X 100
What does 100% atom economy mean?
It means that all the atoms in the reactants have been turned into useful (desired) products.
The higher the atom economy the ‘greener’ the process.
What are titrations used for?
Can be used to accurately add just the right volume of acid to neutralise an alkali.
What’s the method for a titration?
- Using a pipette, measure out a set volume of the alkali into a flask. Add a few drops of an indicator. (Phenolphthalein / methyl orange).
- Fill a burette with a standard solution (known concentration) of acid.
- Use the burette to add the acid to the alkali a bit at a time. Swirl the flask regularly. Add a drop at a time when you think the alkalis almost neutralised.
- The indicator changes colour when all the alkali has been neutralised. Phenolphthalein is pink in alkalis but colourless in acids.
- Record the volume of acid used to neutralise the alkali.
- Repeat this process a few times, making sure you get similar results. You can then take the mean.
What’s the equation for concentration?
Number of moles / volume of solution
What do fuel cells use?
Fuel and oxygen to produce electrical energy.
What is a fuel cell?
Its an electrical cell that’s supplied with a fuel and oxygen and uses energy from the reaction between them to produce electrical energy efficiently.
What do hydrogen-oxygen use as fuel?
Hydrogen
What are the advantages of hydrogen-oxygen?
They’re more efficient than power stations or batteries at producing electricity.
Electricity is generated directly from he reaction (so no turbines/generators)
Unlike a car engine or a fossil fuel burning power station, there are no moving parts, so energy isn’t lost through friction.
Fuel cell vehicles don’t produce any conventional pollutants - no greenhouse gases, no nitrogen oxides, no sulfur dioxide, no carbon monoxide.
